UVA 11090 Going in Cycle!!

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  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <queue>
  5 #include <vector>
  6 #define maxn 60
  7 using namespace std;
  8 vector<int> v,next;
  9 vector<double> w;
 10 double d[maxn];
 11 int first[maxn],inq[maxn],cnt[maxn];
 12 int n,m,e,ub;
 13 
 14 void init()
 15 {
 16     ub = 0;
 17     e = 0;
 18     v.clear();
 19     w.clear();
 20     next.clear();
 21     memset(first,-1,sizeof(first));
 22 }
 23 
 24 void Read_Graph()
 25 {
 26     int i,a,b,c;
 27     for(i = 0;i < m;i++)
 28     {
 29         scanf("%d%d%d",&a,&b,&c);
 30         ub = max(ub,c);
 31         w.push_back(c);
 32         v.push_back(b);
 33         next.push_back(first[a]);
 34         first[a] = e;
 35         e++;
 36     }
 37 }
 38 
 39 bool negativeCycle()
 40 {
 41     queue<int> q;
 42     memset(cnt,0,sizeof(cnt));
 43     memset(inq,0,sizeof(inq));
 44     int i;
 45     for(i = 1;i <= n;i++)
 46     {
 47         q.push(i);
 48         d[i] = 0;
 49     }
 50     inq[1] = 1;
 51     while(!q.empty())
 52     {
 53         int ith = q.front();
 54         q.pop();
 55         inq[ith] = 0;
 56         for(i = first[ith];i != -1;i = next[i])
 57         {
 58             if(d[v[i]] > d[ith] + w[i])
 59             {
 60                 d[v[i]] = d[ith] + w[i];
 61                 if(!inq[v[i]])
 62                 {
 63                     q.push(v[i]);
 64                     inq[v[i]] = 1;
 65                     if(++cnt[v[i]] > n) return true;
 66                 }
 67             }
 68         }
 69     }
 70     return false;
 71 }
 72 
 73 bool test(double x)
 74 {
 75     int i;
 76     bool ret;
 77     for(i = 0;i < e;i++)
 78         w[i] -= x;
 79     ret = negativeCycle();
 80     for(i = 0;i < e;i++)
 81         w[i] += x;
 82     return ret;
 83 }
 84 
 85 int main()
 86 {
 87     int N;
 88     scanf("%d",&N);
 89     for(int ncase = 1;ncase <= N;ncase++)
 90     {
 91         scanf("%d%d",&n,&m);
 92         init();
 93         Read_Graph();
 94         double middle,left = 0,right = ub;
 95         if(!test(ub + 1))
 96         {
 97             printf("Case #%d: No cycle found.\n",ncase);
 98             continue;
 99         }
100         while(right - left > 1e-3)
101         {
102             middle = left + (right - left) / 2;
103             if(test(middle))    right = middle;
104             else    left = middle;
105         }
106         printf("Case #%d: %.2f\n",ncase,left);
107     }
108     return 0;
109 }

 

posted @ 2012-12-15 17:42  浙西贫农  阅读(202)  评论(0)    收藏  举报